The present invention relates to a wire-bonding method, a wire-bonding apparatus, and a semiconductor device which is produced by the wire-bonding method. More particularly, it relates to techniques which are effective when applied to wire-bonding technology employing a coated wire having the surface of a metal wire coated with an insulator, as well as semiconductor devices employing the coated wire.
A wire is used for the connection between the semiconductor chip and lead of a resin-encapsulated semiconductor device. The wire is joined by a wire-bonding apparatus.
The wire is wound round a spool with which the bonding apparatus is furnished, and it is supplied from the spool to a bonding space through a tensioner, a wire clamper, a bonding tool, etc. The bonding apparatus is so constructed that the wire formed with a ball at the supply-side front end thereof is joined to the external terminal (bonding pad) of the semiconductor chip (pellet), whereupon the rear-end side of the wire of predetermined length is joined to the lead which is an external drawing-out lead formed in a lead frame. The bonding method of this type is called "ball bonding". The ball at the front end of the wire on the supply side thereof is formed by thermal energy generated in such a way that an electric torch (an arc electrode) is brought near to the supply-side front end of the wire so as to strike electric arcs.
As the wire, there is a tendency to use a coated wire. The coated wire is such that the surface of a metal wire of gold (Au), copper (Cu) or the like is coated with an electric insulator made of a resin material such as polyurethane resin or polyimide resin. This coated wire has the feature that, when the semiconductor device has been encapsulated with a resin for the purpose of packaging, a defective continuity ascribable to the contact between the individual wires, a defective continuity ascribable to the contact between the wire and the semiconductor chip, etc. can be prevented by the coating of the electric insulator.
In joining the coated wire to the wire-bonding part, namely, the external terminal of the semiconductor chip or the lead, the insulator of the coating at the part of the coated wire to be joined needs to be removed. The removal of the insulator is naturally intended to ensure the electrical connection and perfect continuity between the coated wire and the external terminal or lead.
A technique for removing the insulator of the coated wire is disclosed in the official gazette of Japanese Patent Application Laid-Open No. 194735/1986, the application of which was filed by the assignee of the present application. This technique consists in that the insulator of the bonding part of the coated wire is irradiated with a laser beam so as to be decomposed (melted) and removed.